Zum chemischen Transport der Wolframoxide WO2 und W18O49 mit HgI2. Experimente und Modellrechnungen

On the Chemical Transport of Tungsten Oxides WO₂ and W₁₈O₄₉ with Hgl₂. Experiments and Calculations Transport experiments with WO₂ or W + WO₂ or WO₂ + W₁₈O₄₉ show that HgI₂ is a transport agent as suitable as I₂. We observed transport rates up to 47 mg/h. We investigated the dependence of the transport rate on the concentration of the transport agent n°(HgI₂) as well as on the temperature. We also investigated the time dependence of the transport rates during transport experiments on a “transport balance”. Starting with WO₂ + W₁₈O₄₉, WO₂ is transported before W₁₈O₄₉. Thermodynamic calculations show that transport of W₁₈O₄₉ is understandable if the presence of small amounts of H₂O from the quartz glass wall are taken into consideration, while transport of WO₂ is possible with HgI₂ in the presence of H₂O as well as in absence of H₂O. is the most important reaction for the transport of WO₂.     

一维纳米材料Cs0.2WO3和W18O49长度与红外吸收关联性的Mie散射理论推导及实验验证

研究表明二元、三元钨基氧化物的红外吸收性能具有尺寸和形貌依赖性,但还没有普适性的物理学机理及计算方法。本工作基于Mie散射理论,推导了一维材料的长度与光吸收性能之间的关系,通过理论推导计算和实验验证,探究了纳米钨基氧化物的红外吸收性能与颗粒长度的关联性。首先,基于Mie散射理论的推演和计算,揭示了增加纳米Cs_(0.2)WO_3和W_(18)O_(49)材料长度可适度提高其近红外吸收性能的规律。其次,测试了合成的不同长度Cs_(0.2)WO_3纳米棒和W_(18)O_(49)纳米线的红外吸收性能,结果与理论计算及模拟相吻合。其中在2 500～20 000 nm波长范围内Cs_(0.2)WO_3纳米棒和W_(18)O_(49)纳米线随长度的变化趋势不同,Cs_(0.2)WO_3纳米棒的红外吸收性能随长度的增加而增加,而W_(18)O_(49)纳米线的红外吸收性能随长度的增加而减弱。Cs_(0.2)WO_3纳米棒和W_(18)0O_9纳米线的光热效应均随长度的增加而增加,增幅分别达18.5%和12.7%,再次验证了长度效应。     

The Mixed Valence Tungsten(IV,V) Compound Na[W2O2Br6]

The reaction of W₆Br₁₂, NaBr, and WO₂Br₂ in the presence of Br₂ in a sealed silica tube yields Na[W₂O₂Br₆] together with WOBr₄ and WO₂Br₂ in the low temperature zone (temperature gradient 1030/870 K). Na[W₂O₂Br₆] crystallizes orthorhombically in the space group Immm (no. 71) with a = 3.775 Å, b = 10.400 Å, c = 13.005 Å and Z = 2. Pairs of condensed trans-[WO₂Br₄] octahedra with a common Br₂ edge form along [100] double chains [W₂O_4/2Br₆]^1– via the oxygen atoms. The mixed valent tungsten atoms are bonded to W₂ pairs with a 2 c–3 e bond (d(W–W) = 2.946 Å, d(W–O) = 1.888 Å, d(W–Br^b) = 2.537 Å, d(W–Br^t) = 2.535 Å, ∢O–W–O = 177.4°, ∢Br^b–W–Br^b (endocyclic) = 109.0°). The Na⁺ cations connect the anionic double chains to form two-dimensional layers parallel (001), which interact by van der Waals forces. The cations are eightfold coordinated by a cube of the terminal Br^t ligands of the polymeric anions (d(Na–Br) = 3.138 Å). Na[W₂O₂Br₆] may be discussed as an intercalation compound of the oxide bromide WOBr₃.     

Darstellung,Struktur und Schwingungsspektren der Oxofluorowolframate(VI) Cs2[WO3F2] und Cs3[W2O4F7]

Synthesis, Structure, and Vibrational Spectra of the Oxofluorotungstates(VI) Cs₂[WO₃F₂] and Cs₃[W₂O₄F₇] Cs₂[WO₃F₂] crystallizes from a melt with the same composition. The orthorhombic unit cell with a = 6.779(2), b = 7.668(1) and c = 11.626(3) Å, space group Pn2₁a, contains 4 formula units. The WO₃F₂^2? anion is polymer, W octahedrally coordinated according to the results of the X-ray crystal structure determination. Planar dioxodifluoro groups are linked into chains by oxygen atoms. The lengths of the W? O bonds are alternating. Cs₃[W₂O₄F₇] crystallizes trigonal, space group P3 m1, with a = 21.118(4) and c = 8.434(2) Å, Z = 9. The structure consists of two sets of crystallographically non equivalent dimeric anions with the formula [O₂F₃W? F? WO₂F₃]^3?. Part of the ligand atoms are disordered. The vibrational spectra of both compounds show the presence of cis-dioxo groups of the terminal ligands.     

Neue Heteropolyanionen des M2X2W20‐Typs mit Antimon(III) als Heteroatom

New Heteropolyanions of the M₂X₂W₂₀ Structure Type with Antimony(III) as a Heteroatom The syntheses of two new heteropolyanions of the M₂X₂W₂₀ structure type are presented. They are characterized by X‐ray structure analysis and vibrational spectra. Na₆(NH₄)₄[Zn₂(H₂O)₆(WO₂)₂(SbW₉O₃₃)₂]·36H₂O (1) is monoclinic (P2₁/n) with a = 12.873(3)Å, b = 25.303(4)Å, c = 15.975(4)Å and β = 91.99(3)°. Na₁₀[Mn₂(H₂O)₆(WO₂)₂(SbW₉O₃₃)₂]·40H₂O (2) also crystallizes in the space group P2₁/n with a = 12.892(3)Å, b = 25.219(5)Å, c = 16.166(3)Å and β = 94.41(3)°. Both polyanions are isostructural to anions of this structure type containing other heteroatoms. They are built up by two β‐B‐SbW₉ fragments, which are derived from defect structures of the Keggin anion. These subÍunits are connected by two formal WO₂ groups with further stabilization by addition of two M(H₂O)₃ groups (M = Zn^II, Mn^II, Fe^III, Co^II) leading to the M₂X₂W₂₀‐type heteropolytungstates.     

Über hexagonale Perowskite mit Kationenfehlstellen. XII. Strukturbestimmung an Ba6W4□2O18

On Hexagonal Perovskites with Cationic Vacancies. XII. Structure Determination on Ba₆W₄□₂O₁₈ The stacking polytype Ba₆W₄□₂O₁₈ is the first oxidic variant of the Cs₃Tl₂Cl₉-type. The structure determination gave for the space group R3 c with the sequence (h)₆, Z = 3, the refined, intensity related R′ value of 6.8%. The octahedral net consists of groups of two face sharing WO₆ octahedra (W₂O_6/2;O₆), which are in the (110) plane displaced against each other. In the doublé octahedra the tungsten atoms are shifted away from their ideal central position (W–W: 2.32₇ Å) with the result, that the W–W distance has increased to 2.90₅ Å.     

氧化钨纳米棒团簇的制备及电催化性能

以氯化钨为前驱体,通过溶剂热法制备了WO₃和W₁₈O₄₉并将其应用在染料敏化太阳能电池(dye-sensitized solar cells,DSSCs)和电解水析氢反应(hydrogen evolution reaction,HER)中。通过X射线衍射仪(XRD)、场发射扫描电子显微镜(FESEM)和透射电子显微镜(TEM)对WO₃和W₁₈O₄₉的结构和形貌进行表征。结果表明：WO₃和W₁₈O₄₉均为单斜相,其形貌表现为定向排列的纳米棒组成的团簇。X射线光电子能谱(XPS)和电子顺磁共振(EPR)表明W₁₈O₄₉中含有丰富的氧空位。基于氧空位优异的电化学特性,W₁₈O₄₉对电极组装的DSSC获得了7.41%的光电能量转换效率(power conversion efficiency,PCE),高于WO     

Hydrolysis of ammonium oxofluorotungstates: A F, O and W NMR study

Fluorine-19 and natural abundance ¹⁷O and ¹⁸³W NMR spectroscopy were employed for the characterization of aqueous solutions of (NH₄)₂WO₂F₄ and (NH₄)₃WO₃F₃. Dissolution of the (NH₄)₂WO₂F₄ complex is accompanied by its partial acid hydrolysis to give the trans(mer)-dimer, [W₂O₅F₆]⁴⁻, and unreacted cis-[WO₂F₄]²⁻. The cis(fac)-[W₂O₅F₆]⁴⁻ anion is the major soluble product resulting from the alkaline hydrolysis of (NH₄)₂WO₂F₄ along with the isolation of the solid (NH₄)₂WO₃F₂. In addition, the edge-bridging dimer, [W₂O₆F₄]⁴⁻, and the cyclic trimer, [W₃O₉F₆]⁶⁻, are also suggested as hydrolysis products. Decomposition of (NH₄)₃WO₃F₃ occurs in aqueous solution to give NH₄WO₃F.     

Vacancy Engineering of Iron-Doped W18O49 Nanoreactors for Low-Barrier Electrochemical Nitrogen Reduction

The electrochemical nitrogen reduction reaction (NRR) is a promising energy-efficient and low-emission alternative to the traditional Haber–Bosch process. Usually, the competing hydrogen evolution reaction (HER) and the reaction barrier of ambient electrochemical NRR are significant challenges, making a simultaneous high NH₃ formation rate and high Faradic efficiency (FE) difficult. To give effective NRR electrocatalysis and suppressed HER, the surface atomic structure of W₁₈O₄₉, which has exposed active W sites and weak binding for H₂, is doped with Fe. A high NH₃ formation rate of 24.7 μg h⁻¹ mg_cat⁻¹ and a high FE of 20.0 % are achieved at an overpotential of only −0.15 V versus the reversible hydrogen electrode. Ab initio calculations reveal an intercalation-type doping of Fe atoms in the tunnels of the W₁₈O₄₉ crystal structure, which increases the oxygen vacancies and exposes more W active sites, optimizes the nitrogen adsorption energy, and facilitates the electrocatalytic NRR.     

Zur Präparation und Struktur gemischtvalenter Niob-Wolframoxide der Zusammensetzung (Nb,W)17O47

Preparation and Structure of Niobium Tungsten Oxides (Nb,W)₁₇O₄₇ with Mixed Valency The formal substitution of 2Nb⁵⁺ by Nb⁴⁺ or W⁴⁺, respectively, and W⁶⁺ leads to tungsten niobium oxides (Nb,W)₁₇O₄₇ with mixed valency. The phases Nb_8-nW_9+nO₄₇ with n = 1 to 5 could be obtained by heating (1 250°) mixtures of NbO₂ or WO₂, respectively, with Nb₂O₅ and WO₃. The products crystallize with the structure of Nb₈W₉O₄₇. This is proved by X-ray powder diffraction and transmission electron microscopy. A further decrease of the Nb-content results in two-phase products.     

Characteristic features of polytypism in compounds with the La18W10O57‐type structure

Crystals with the La₁₈W₁₀O₅₇‐type structure (6H and 5H polytypes) were obtained by a self‐flux method from high‐temperature solutions. Some of the crystal samples were studied by single‐crystal X‐ray structure analysis. The diffraction patterns indicated that two phases co‐exist in each sample. The hexagonal lattices have a common period of a ≈ 9.0 Å and are non‐equal in length but have equally oriented superstructure periods 6c (phase I) and 5c (phase II), c ≈ 5.4 Å. The structures of phases I and II were solved in the symmetry groups P2c and P321, respectively, based on the X‐ray data for crystals I and II, with predominant content of the first and second phase. The motif of isolated WO₆ prisms with W atoms on the cell edges is common to both phases. WO₆ octahedra, both isolated and joined by faces, are distributed along the c axis within the unit cells. Phase I contains extra layers of isolated WO₆ octahedra compared to phase II. Tungsten sites in joined octahedra are disordered and partially occupied. Disordering is more expressed in phase II, which in return contains rather more W and O per atom of La. The refined chemical compositions are La₁₈W₁₀O₅₇ for I and La₁₅W_8.5O₄₈ for II.     

Vacancy Engineering of Iron‐Doped W18O49 Nanoreactors for Low‐Barrier Electrochemical Nitrogen Reduction

The electrochemical nitrogen reduction reaction (NRR) is a promising energy‐efficient and low‐emission alternative to the traditional Haber–Bosch process. Usually, the competing hydrogen evolution reaction (HER) and the reaction barrier of ambient electrochemical NRR are significant challenges, making a simultaneous high NH₃ formation rate and high Faradic efficiency (FE) difficult. To give effective NRR electrocatalysis and suppressed HER, the surface atomic structure of W₁₈O₄₉, which has exposed active W sites and weak binding for H₂, is doped with Fe. A high NH₃ formation rate of 24.7 μg h^?1 mg_cat^?1 and a high FE of 20.0 % are achieved at an overpotential of only ?0.15 V versus the reversible hydrogen electrode. Ab initio calculations reveal an intercalation‐type doping of Fe atoms in the tunnels of the W₁₈O₄₉ crystal structure, which increases the oxygen vacancies and exposes more W active sites, optimizes the nitrogen adsorption energy, and facilitates the electrocatalytic NRR.     

[Rh(NH3)5Cl]WO4 crystal structure

At T 150 K the crystal structure of [Rh(NH₃)₅Cl]WO₄ is studied: a = 11.2374(4) Å, b = 8.4857(3) Å, c = 10.5326(3) Å, V = 1004.36(6) ų, space group Pnma, Z= 4, d _x = 3.117 g/cm³. In the structure, complex ions are bound by N—H…O hydrogen bonds, with the shortest ones of 2.85–2.94 Å. Ionic packing is shown to be considered as rhombohedral with a _t ≈ 5.26 Å, α_t ≈ 106°. Thermal properties of the salt are studied in the hydrogen atmosphere. The product of thermal decomposition at 750°C is a mixture of three solid solutions of Rh_x W _1- x based on fcc, bcc, and hcp structures. All the obtained phases are nanocrystalline. The sizes of coherent scattering regions are 10–12 nm.     

Growth of KY(WO4)2 single crystal: investigation of the WO3 rich region in the K2O-Y2O3-WO3 ternary system. 2 — The KY(WO4)2 crystallisation field

In order to determinate the best crystal growth conditions for KY(WO₄)₂ single-crystals, the investigation of the K₂O-Y₂O₃-WO₃ ternary system was undertaken by the study of three isoplethic sections (K₂W₄O₁₃-Y₂O₃, K₂WO₄-KY(WO₄)₂, K₂W₂O₇-KY(WO₄)₂). The stability domain and the crystallisation field of the compound were then defined: KY(WO₄)₂ is not stoichiometric and melts congruently for the composition 0.81(K₂O.4WO₃)−0.19Y₂O₃ The low temperature phase belongs to the monoclinic system (s.g. C2/c) with a=10.65(1)Å, b=10.34(1)Å, c=7.54(1)Å, β=130.5(1)°. Its crystallisation field was delimited in temperature and composition: an α-KY(WO₄)₂ crystal can grow if x_Y2O3≤0.175.     

Ein neuer Strukturtyp am Lanthanoid-Oxowolframat FeCe(WO4)W2O8 = FeCe(WO4)3

A New Structure Type for the Rare Earth Oxotungstate FeCe(WO₄)W₂O₈ = FeCe(WO₄)₃ Single crystals of the hitherto unknown compound FeCe(WO₄)₃ have been prepared by crystallization from melts of Fe₂O₃, CeO₂ and WO₃. It crystallizes with triclinic symmetry, space group P1 , a = 7,486(3); b = 7,528(1); c = 16,502(4) Å, α = 101,00(2); β = 96,62(3); γ = 98,62°; Z = 2. Tungsten shows octahedral and tetrahedral coordination by oxygen. The crystal structure is characterized by layers related to the Scheelite and Wolframite type. Thermogravimetric measurements led to a lost of oxygen during reaction. It results in a decrease of the oxidation states of Fe³⁺ and Ce⁴⁺ respectively, as will be discussed using magnetic measurements and calculations of the Coulomb terms of lattice energy. The structure contains a one-fold coordinated oxygen.     

Zur Koordinationschemie von cis-Trioxowolfram(VI)-Komplexen. Die Kristallstrukturen von LWO3 · 3 H2O, [L′WO2(OH)]Br, [LWO2Br]Br, [L2W2O5](S2O6) · 4 H2O und [LWO2(μ-O)WO(O2)2(OH2)] (L = 1,4,7-Triazacyclononan; L′ = 1,4,7-Trimethyl-1,4,7-triazacyclononan)

Coordination-chemistry of cis-Trioxotungsten(VI) Complexes. Crystal Structures of LWO₃ · 3 H₂O, [L′WO₂(OH)]Br, [LWO₂Br]Br, [L₂W₂O₅](S₂O₆) · 4 H₂O and [LWO₂(μ-O)WO(O₂)₂(OH₂)] (L = 1,4,7-Triazacyclonane; L′ = 1,4,7-Trimethyl-1,4,7-triazacyclononane) The cyclic triamines 1,4,7-triazacyclononane (L; C₆H₁₅N₃) and 1,4,7-trimethyl-1,4,7-triazacyclononane (L′; C₉H₂₁N₃) react in aqueous solution with WO₃ affording LWO₃ · 3 H₂O, 1 , and L′WO₃ · 3 H₂O, respectively, which yield [L′WO₂(OH)]Br, 2 , and [LWO₂Br]Br, 3 , in concentrated HBr solutions. In aqueous CH₃SO₃H solution 1 dimerizes. The iodide and dithionate 4 salts of [L₂W₂O₅]²⁺ have been isolated. In 35% H₂O₂ complex 1 yields the neutral species [LWO₂(μ-O)WO(O₂)₂(H₂O)] 5 . The crystal structures of 1 – 5 have been determined by X-ray analysis. Crystal data: 1 : P2₁/c; a = 7.729(2), b = 14.887(3), c = 10.774(2) Å, β = 90.77(2)°, Z = 4; 2 : Cc; 8.910(3), b = 12.220(6), c = 13.279(6) Å, β = 101.31(3)°, Z = 4; 3 : Cmc2₁, a = 8.857(5), b = 12.062(7), c = 11.218(7) Å, Z = 4; 4 : Cc, a = 17.601(7), b = 12.906(7), c = 14.107(8) Å, β = 124.08(4)°, Z = 4; 5 : P2₁2₁2₁; a = 8.452(4), b = 11.301(6), c = 13.750(6) Å, Z = 4.     

Notes on phases occurring in the binary tungsten-oxygen system

The phases occurring in the binary tungsten-oxygen system in the composition region WO₃WO₂ have been clarified by electron microscopy and powder X-ray diffraction in the temperature range from 723 to 1373 K. There are five structure types in the binary system, besides WO₃, viz., the {102} CS structures, the {103} CS structures, W₂₄O₆₈, W₁₈O₄₉, and WO₂. The {102} and {103} CS structures, and W₂₄O₆₈ structures, were always disordered and true equilibrium was not achieved even after 5 months of heating at 1373 K. The lowest temperature for the formation of the CS phases was of the order of 873 K, and the disordered W₂₄O₆₈ structure formed at somewhat higher temperatures. The formation of the latter phase was also slower than the formation of the CS phases. The results suggest that elastic strain energy is of importance in controlling the microstructures found in the nonstoichiometric regions.     

Infrared and X-ray studies of hydrogen intercalation in different tungsten trioxides and tungsten trioxide hydrates

Hydrogen intercalation via spillover reaction in various tungsten trioxides leads to the formation of blue hydrogen bronzes. These reversible reactions induce changes in the W-O bond system while maintaining the W-O skeleton. The effect of the intercalation process on the host crystalline structure has been studied with respect to the ν(O-W-O) stretching vibration changes and lattice parameter variations by means of infrared and X-ray diffraction measurements. Among the main results, the intercalation process is shown to be strongly influenced by the structural type of the host compound as well as its amorphous versus crystalline nature. For instance, for the ReO₃ type oxides (monoclinic and cubic WO₃) and hexagonal WO₃, ν(O-W-O) shifts to higher frequency are assigned to a shortening effect of W-O bonds. A W-O bond system arrangement is also measured for the crystallized and amorphous hydrates WO₃ · H₂O, but no detectable changes could be found in the pyrochlore WO₃ and in the hydrate WO₃·1/3 H₂O. Received: 5 March 1997 / Accepted: 21 May 1997     

Neue Heteropolyanionen des Wolframs mit Vanadium(IV) als Heteroatom

New Heteropolyanions of Tungsten with Vanadium(IV) as a Heteroatom The syntheses of two new heteropolyanions with vanadium as heteroatom are presented. They are characterized by X‐ray structure analysis and vibrational spectra. ((CH₃)₄N)₆Na₄[(VO(H₂O)₂)₂(WO₂)₂(BiW₉O₃₃)₂]·18H₂O (1) crystallises in the triclinic crystal system (P1¯) with a = 13.299(3)Å, b = 13.554(3)Å, c = 18.620(4)Å and α = 90.22(3)°, β = 91.99(3)°, γ = 119.16(3)°. Na_5.4K_6.6[(VO)₃(AsW₉O₃₃)₂]·29H₂O ( 2 ) crystallises in the hexagonal space group P6₃/mmc with a = 15.124(3)Å and c = 24.209(5)Å. The polyanion in 1 is isostructural to anions of the M₂X₂W₂₀‐typ with other heteroatoms. They are built up by two β‐B‐[SbW₉O₃₃] fragments, which are derived from defect structures of the Keggin anion. These subunits are connected by two formal WO₂ groups with further stabilisation by addition of two M(H₂O)₃ groups leading to the M₂X₂W₂₀‐type heteropolytungstates. The anion in 2 is a new example of the M₃X₂W₁₈‐type, which contains two α‐B‐[XW₉O₃₃]‐units connected via a belt of three transition metal atoms.